Some eeproms in the at24 family do not roll over page reads,
e.g. the Microchip 24AA16/24LC16B. On those eeproms, reads
that straddle block boundaries will not work correctly.
Solution:
Implement read rollover in the driver. To enable it, add the
AT24_FLAG_NO_RDROL flag to the eeprom entry in the
device_id table, or add 'no-read-rollover' to the eeprom
devicetree entry.
Signed-off-by: Sven Van Asbroeck <svendev@xxxxxxxx>
---
.../devicetree/bindings/eeprom/eeprom.txt | 5 +++
drivers/misc/eeprom/at24.c | 46 +++++++++++-----------
include/linux/platform_data/at24.h | 1 +
3 files changed, 28 insertions(+), 24 deletions(-)
diff --git a/Documentation/devicetree/bindings/eeprom/eeprom.txt b/Documentation/devicetree/bindings/eeprom/eeprom.txt
index afc0458..301bc7e 100644
--- a/Documentation/devicetree/bindings/eeprom/eeprom.txt
+++ b/Documentation/devicetree/bindings/eeprom/eeprom.txt
@@ -36,6 +36,11 @@ Optional properties:
- read-only: this parameterless property disables writes to the eeprom
+ - no-read-rollover: supported on the at24 eeprom family only.
+ This parameterless property indicates that the
+ eeprom does not support auto read rollover. Please consult
+ the manual of your device.
+
Example:
eeprom@52 {
diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index 764ff5df..ef4197c 100644
--- a/drivers/misc/eeprom/at24.c
+++ b/drivers/misc/eeprom/at24.c
@@ -192,26 +192,22 @@ struct at24_data {
* set the byte address; on a multi-master board, another master
* may have changed the chip's "current" address pointer.
*
- * REVISIT some multi-address chips don't rollover page reads to
- * the next slave address, so we may need to truncate the count.
- * Those chips might need another quirk flag.
- *
- * If the real hardware used four adjacent 24c02 chips and that
- * were misconfigured as one 24c08, that would be a similar effect:
- * one "eeprom" file not four, but larger reads would fail when
- * they crossed certain pages.
+ * In case of chips that don't rollover page reads, truncate the count
+ * to the nearest page boundary. This might result in the
+ * at24_eeprom_read_XXX functions reading fewer bytes than requested,
+ * but this is compensated for in at24_read().
*/
static struct i2c_client *at24_translate_offset(struct at24_data *at24,
- unsigned int *offset)
+ unsigned int *offset, size_t *count)
{
- unsigned i;
-
- if (at24->chip.flags & AT24_FLAG_ADDR16) {
- i = *offset >> 16;
- *offset &= 0xffff;
- } else {
- i = *offset >> 8;
- *offset &= 0xff;
+ unsigned int i, bits, remainder;
+
+ bits = (at24->chip.flags & AT24_FLAG_ADDR16) ? 16 : 8;
+ i = *offset >> bits;
+ *offset &= AT24_BITMASK(bits);
+ if ((at24->chip.flags & AT24_FLAG_NO_RDROL) && count) {
+ remainder = BIT(bits) - *offset;
+ *count = min(*count, remainder);
}
return at24->client[i];
@@ -224,7 +220,7 @@ static ssize_t at24_eeprom_read_smbus(struct at24_data *at24, char *buf,
struct i2c_client *client;
int status;
- client = at24_translate_offset(at24, &offset);
+ client = at24_translate_offset(at24, &offset, &count);
if (count > io_limit)
count = io_limit;
@@ -258,7 +254,7 @@ static ssize_t at24_eeprom_read_i2c(struct at24_data *at24, char *buf,
u8 msgbuf[2];
memset(msg, 0, sizeof(msg));
- client = at24_translate_offset(at24, &offset);
+ client = at24_translate_offset(at24, &offset, &count);
if (count > io_limit)
count = io_limit;
@@ -307,7 +303,7 @@ static ssize_t at24_eeprom_read_serial(struct at24_data *at24, char *buf,
u8 addrbuf[2];
int status;
- client = at24_translate_offset(at24, &offset);
+ client = at24_translate_offset(at24, &offset, &count);
memset(msg, 0, sizeof(msg));
msg[0].addr = client->addr;
@@ -360,7 +356,7 @@ static ssize_t at24_eeprom_read_mac(struct at24_data *at24, char *buf,
u8 addrbuf[2];
int status;
- client = at24_translate_offset(at24, &offset);
+ client = at24_translate_offset(at24, &offset, &count);
memset(msg, 0, sizeof(msg));
msg[0].addr = client->addr;
@@ -415,7 +411,7 @@ static ssize_t at24_eeprom_write_smbus_block(struct at24_data *at24,
struct i2c_client *client;
ssize_t status = 0;
- client = at24_translate_offset(at24, &offset);
+ client = at24_translate_offset(at24, &offset, NULL);
count = at24_adjust_write_count(at24, offset, count);
loop_until_timeout(timeout, write_time) {
@@ -442,7 +438,7 @@ static ssize_t at24_eeprom_write_smbus_byte(struct at24_data *at24,
struct i2c_client *client;
ssize_t status = 0;
- client = at24_translate_offset(at24, &offset);
+ client = at24_translate_offset(at24, &offset, &count);
loop_until_timeout(timeout, write_time) {
status = i2c_smbus_write_byte_data(client, offset, buf[0]);
@@ -468,7 +464,7 @@ static ssize_t at24_eeprom_write_i2c(struct at24_data *at24, const char *buf,
ssize_t status = 0;
int i = 0;
- client = at24_translate_offset(at24, &offset);
+ client = at24_translate_offset(at24, &offset, NULL);
count = at24_adjust_write_count(at24, offset, count);
msg.addr = client->addr;
@@ -569,6 +565,8 @@ static void at24_get_pdata(struct device *dev, struct at24_platform_data *chip)
if (device_property_present(dev, "read-only"))
chip->flags |= AT24_FLAG_READONLY;
+ if (device_property_present(dev, "no-read-rollover"))
+ chip->flags |= AT24_FLAG_NO_RDROL;
err = device_property_read_u32(dev, "pagesize", &val);
if (!err) {
diff --git a/include/linux/platform_data/at24.h b/include/linux/platform_data/at24.h
index 271a4e2..a5804f1 100644
--- a/include/linux/platform_data/at24.h
+++ b/include/linux/platform_data/at24.h
@@ -50,6 +50,7 @@ struct at24_platform_data {
#define AT24_FLAG_TAKE8ADDR BIT(4) /* take always 8 addresses (24c00) */
#define AT24_FLAG_SERIAL BIT(3) /* factory-programmed serial number */
#define AT24_FLAG_MAC BIT(2) /* factory-programmed mac address */
+#define AT24_FLAG_NO_RDROL BIT(1) /* chip does not rollover page reads */
void (*setup)(struct nvmem_device *nvmem, void *context);
void *context;
--
1.9.1
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